01 Altima GXE

[polarbyte]

Hi, hope someone can help. My baby is 7 years old now and decided to be fussy. For the last 2 years my check engine light has come on and then gone off. Usually on for about a week to a whole month. Then off for about 4 to 6 months. Now it's staying on. Checked it, got codes for catalytc convertor and knock sensor. After reading some blogs, I get the impression it could be the EGR valve. So....

How do I check the knock sensor with a voltmeter to ensure it is working?

How do you check a EGR valve?

And how do you change the bulb in the back window brake light?

Within the last 6 months I've put in a new alternator, tune up, oil change, head gasket, and air filter.

Thanks for any help you can offer.

-Mattie